8.5GB??? Never heard of one before and checked Wikipedia to help. I see in there it says:
DVD-R DL (DL stands for Dual Layer[1]), also called DVD-R9, is a derivative of the DVD-R format standard. DVD-R DL discs hold 8.54 GB (7.96 GiB) per side by utilizing two recordable dye layers, each capable of storing nearly the 4.7 gigabyte (GB) (4.38 GiB) of a single layer disc -almost doubling the total disc capacity. Discs can be read in many DVD devices (older units are less compatible) and can only be written using DVD-R DL compatible recorders
So your search would be for the keywords DVD-DV9 and DVD-R DL when looking for a DVD writer for your LG Mdiscs. Personally a quick search didn't give me anything, and I am thinking this may be a 'specialty' item costing hundreds if not thousands, usually reserved for specialty needs like Video Production Specialists, Medical Data Recorders, etc. that would do such high level use.